Police say four men in custody over the bashing death of a man at Sydney airport yesterday are likely to be charged with affray.

Botany Bay Police say it appears a group of men got off a plane at the domestic terminal where they were confronted by a another group of men, believed to be bikies.

Police say a fight broke out and some of the men picked up metal bollards from the airport check-in area and used them to bash the victim - a 29-year-old from Lakemba in Sydney's south-west.

Detective Inspector Peter Williams says the victim died a short time later in hospital.

"At this point in time we are investigating a murder. It would appear that up to 15 men [were] involved in a melee that ultimately resulted in a man being killed," he said.

The men in custody are aged 25 from Auburn and 21 from Pemulwuy, in Sydney's west, and 22 from Casula and 22 from Ingleburn, in Sydney's south-west.

Investigations are continuing. Detective Inspector Williams says police are viewing CCTV footage and talking to witnesses to piece together what happened.

He has described it as a disgraceful and cowardly act.

Earlier, witness Phil Crew said the group closed in on the victim using the metal bollards as weapons.

"It looked like two people fighting at first, and then all of a sudden a whole rush of guys came through the crowd, picked up the poles and just started smacking this guy in the head with the poles," he said.

Mr Cruz says the group of men then fled, escaping in taxis.

"They started grabbing the metal poles that break up the check in area and swinging them almost like swords at each other heads," said another witness, Naomi.

"Then one man with a metal pole, another man was on the ground, and [he] started smashing his head."